For operating the hydraulic circuit or the hydraulic consumer a corresponding feed pressure is required. In general, a hydraulic pump generates the appropriate feed pressure by sucking in hydraulic fluid from the tank and providing the feed pressure for operating the hydraulic consumer at its outlet.
Depending on the application, a certain pressure level or a defined volume flow is required for the operation of the hydraulic consumer.
Such application exists in operation of a heave compensation device, also referred to as Active Heave Compensation. Here, it is intended to keep the load steady during the hoisting work despite the heave during deep-sea hoisting. Via the compensation device, the actuation of the hoisting winch is intervened in for this purpose.
The object of the present disclosure aims to develop such hydraulic system, in order to optimize the energy balance of the system by targeted measures.
This object is solved by a hydraulic system for a crane with at least one hydraulic circuit and a constant pressure network. At least one hydraulic circuit includes a hydraulic consumer. For optimizing the energy balance of the entire system, it is provided in accordance with the present disclosure that the required feed pressure for the hydraulic consumer is not generated by a feed pump, but instead the at least one hydraulic circuit is coupled with the constant pressure network via at least one pressure reducer.
Such pressure reducer expediently comprises at least one input and at least one output, wherein via the pressure reducer the pressure and/or volume flow present at the respective connecting points is variable.
Via the pressure reducer a low volume flow with high pressure within the constant pressure network can be convertible into a high volume flow with low pressure within the hydraulic circuit. Hence, the use of a feed pump can be omitted, since the required high volume flow in the hydraulic circuit can be supplied exclusively by the pressure reducer. This measure according to the present disclosure is advantageous in particular where a constant pressure network is installed anyway and the use of the pressure reducer renders the integration of an additional pump superfluous.
In an advantageous embodiment, the pressure reducer comprises at least two interconnected pistons with a suitable ratio of the piston surfaces. In particular, the piston with a smaller piston surface is coupled to the constant pressure network, whereas the large piston surface of the second piston is connected with the hydraulic circuit. By a suitable choice of the surface ratio, the conversion ratio and the volume flow to be achieved can selectively be taken into account.
Furthermore, it can be provided that upon reversal of the flow direction in the hydraulic circuit by which the pressure reducer a power output to the constant pressure network becomes possible. For example when a volume flow is generated at the input of the pressure reducer on the side of the hydraulic circuit, the piston unit is shifted in direction of the constant pressure network and on this side generates a low volume flow with high pressure level.
A reversal of the volume flow in the hydraulic circuit becomes possible for example in that a part of the volume flow or pressure is stored in normal operation. For this purpose, at least one pressure accumulator can be arranged in the hydraulic circuit. When the accumulator releases the stored pressure energy, the volume flow in the hydraulic circuit is reversed, so that this pressure energy can be released back to the constant pressure network via the pressure reducer.
At least one pressure storage device can be a fluid storage device, gas storage device or a storage device for other media. For example, the storage device may be an accumulator. When the form of accumulator does not correspond to the hydraulic fluid used, an air-oil actuator can be incorporated before the accumulator. For example, the storage device may be designed as air pressure accumulator and the pressure energy of the hydraulic fluid is convertible into the corresponding air pressure level via the air-oil actuator.
As hydraulic consumer a hydraulic motor expediently can be used, which may be operable in both flow directions. Hence, the hydraulic motor can be operated in a first direction of rotation by the volume flow generated via the pressure reducer and in an opposite direction of rotation via the stored energy of the storage means.
In a particular embodiment of the present disclosure, a crane cable winch, in particular a deep-sea hoisting cable winch, can be driven via the at least one hydraulic circuit or the hydraulic motor. The hydraulic motor is operated for realizing an active heave compensation whose task is to compensate the heave or heave.
By using a pressure reducer, the hydraulic fluid can be pushed back and forth between the same and possibly an arranged accumulator, which is employed in particular in the operating mode Active Heave Compensation or in similar cyclic operating modes. By the hydraulic system according to the present disclosure, the tank circulation rate can be reduced considerably. In addition, the system is characterized by a particularly efficient energy recovery.
The present disclosure furthermore relates to a crane which includes the hydraulic system according to the present disclosure or an advantageous embodiment of the hydraulic system. The advantages and properties of the crane quite obviously correspond to those of the hydraulic system, so that a renewed description will be omitted at this point.
The crane can include a deep-sea hoisting cable winch which is supplied by a hydraulic drive. In particular, a closed hydraulic circuit with at least one hydraulic motor serves to put the hoisting cable winch in rotation for carrying out a winding or unwinding movement. In addition, the crane can comprise a constant pressure network, which can be supplied by a central hydraulic pump and is used for feeding one or more hydraulic consumers, in particular various crane components.
Furthermore, the crane includes a hydraulic circuit according to the hydraulic system in accordance with the present disclosure. The integrated hydraulic motor can be part of a heave compensation device. The winch here is driven separately by the hydraulic motor, in order to be able to compensate the heave during the actual hoisting work.
Further advantages and details of the present disclosure will be described in detail with reference to two drawings.